Specifies the display screen on which the X Server
is to accept requests from X clients. If the display option is not specified,
X uses the display screen specified by your DISPLAY environment variable.
The display option has the format hostname:number. Using two colons (::)
instead of one (:) indicates that DECnet is to be used for transport.

port

Specifies
the port for which PortNotify events are to be generated when its attributes
are changed using XvSetPortAttribute(3X)
.